Well in that case then perhaps if I plugged the HG612 back in and let it works its magic for a couple of weeks, then ring BT and get them to send out an engy I could "suggest" to him that maybe my modems up the duff and would he pretty please with sugar on top give me a new one. I mean I got the current HG612 for free, the ECI for free and (apart from being forced to pay the postage on it) the HH5 for free so I think I'd like to stick with that tradition.
Edit: This all of course assuming the instability was being caused by the modem being faulty and it isn't just the fact my line can't handle speeds over 20mbit anymore for whatever reason (fault or otherwise, still I suppose even in that case a BT engineer should still come out and fix the damn thing).